Transmission control system for vehicles

ABSTRACT

A transmission control system for vehicle having a transmission fluid actuated clutch means connected to a torque converter and a hydraulic brake means for arresting movement of the vehicle, comprising a source of pressurized fluid, first fluid passageway means connecting said fluid source with said clutch means, a regulator valve means disposed within said first passageway means and automatically controlling hydraulic pressure for said clutch means in response to the prime engine revolution rate, manual means to selectively regulate the passage of pressurized fluid to said clutch means, a second passageway means communicatively connecting said pressure fluid source with said torque converter disposed therein, a relief valve means interposed within said second passageway means and regulating output hydraulic pressure from said torque converter, and a control valve means to make said regulator valve means inoperative in response to activation of the brake pedal of the vehicle.

United States Patent Kitano et a1.

[4 1 May 2, 1972 [54] TRANSMISSION CONTROL SYSTEM FOR VEHICLES [72]Inventors: Shin Kitano; Yutaka Momose, both of Kariya, Japan [73]Assignee: Alsin Seiki Kabushiki Kaisha, Kariya-shi,

Japan [22] Filed: Sept. 1, 1970 21 Appl. No.: 68,607

[30] Foreign Application Priority Data Sept. 3, 1969 Japan ..44/83844Nov. 12, 1969 Japan ..44/90701 [52] US. Cl. ..192/3-33, 74/DlG. 1,74/732, 192/324 [51] Int. Cl ..Fl6d 25/12,Fl6d 33/12,F16d 33/02 [58]Field ofSearch ..l92/3.27, 3.33, 3.24; 74/732, 74/DlG. l

[56] References Cited UNITED STATES PATENTS 3,010,342 11/1961 Kelley..74/732 3,320,967 5/1967 Fiala et a1. ....l92/3.33 3.394.622 7/1968Chana ..74/DIG. l

FOREIGN PATENTS OR APPLICATIONS 1,327,921 1963 France ..l92/3.33 950,0491964 Great Britain ..l92/3.33

Primary Examiner-Mark M. Newman Assistant Examiner-R. B. RothmanAttorney-Berman, Davidson & Berman 57] ABSTRACT A transmission controlsystem for vehicle having a transmission fluid actuated clutch meansconnected to a torque converter and a hydraulic brake means forarresting movement of the vehicle, comprising a source of pressurizedfluid, first fluid passageway means connecting said fluid source withsaid clutch means, a regulator valve means disposed within said firstpassageway means and automatically controlling hydraulic pressure forsaid clutch means in response to the prime engine revolution rate,manual means to selectively regulate the passage of pressurized fluid tosaid clutch means, a second passageway means communicatively connectingsaid pressure fluid source with said torque converter disposed therein,a relief valve means interposed within said second passageway means andregulating outp'ut hydraulic pressure from said torque converter, and acontrol valve means to make said regulator valve means inoperative inresponse to activation of the brake pedal of the vehicle.

10 Claims, 4 Drawing Figures PATENTEDHAY 2 I972 SHEE? 2 BF 2 E$ 58am .6m5); 2329mm A 82 v v t INVENTOR 5H1 N KITA NO YUT'AKO Homes 5 BY v- 1 7@mb WM I I ATTORNEY TRANSMISSION CONTROL SYSTEM FOR VEHICLES The presentinvention relates to a transmission control system, and moreparticularly to a hydraulic control system for a vehicle having atransmission provided with fluid actuated clutch means connected to atorque converter and hydraulic brake means for arresting movement of thevehicle.

An industrial vehicle, such as a fork-lift truck with torquetransmission means having a torque converter, a transmission having aninput shaft driven by the torque converter ,and fluid actuated clutchmeans, is provided with a hydraulic pressure pump to supply the fluidactuated clutch means with pressurized operating fluid, the fluiddischarging capacity of the hydraulic pressure pump being predeterminedto be rather large, so that enough hydraulic pressure may be supplied tothe fluid clutch means even at an idling revolution rate d the primeengine of the vehicle. This creates, however, rather large shocks to thevehicle due to knocking of the prime engine at starting movement of thevehicle, when the fluid clutch means is activated at the idlingrevolution rate of the prime engine of the vehicle. Conventionalfork-lift trucks, and the like, have had such defects as causing damageto their prime engines by shocks created by activating operations oftheir fluid clutch means, and further, causing them to be unable tocarry fragile goods, since in operation of such vehicles very frequentchanges to forward and reverse are required, and also it is necessary tostart and stop such vehicles at low revolution rates of their primeengine.

In order to eliminate the above-mentioned defects, conventionally asystem has been adopted such as to reduce thequantity of pressurizedfluid discharged from the hydraulic pressure pump and also to store itin an accumulator. In this type of system, however, the defect stillremains that in making an urgent start of the vehicle on an inclinedarea with the rate of engine revolution accelerated, a delay inactivating the clutch means caused by the accumulator makes the vehicledescend on the inclined area contrary to the operators intention.

The most important object of the present invention is, therefore, toprovide a hydraulic pressure control system for fluid actuated clutchmeans having a regulator valve means, said regulator valve meansautomatically controlling the quantity of pressure fluid supplied to thefluid actuated clutch means in response to the quantity of pressurefluid supplied from a source of pressure fluid including pressuringmeans therefor, so as to hold low hydraulic pressure for the fluidactuated clutch means at a low engine revolution rate to produce smoothtorque transmission and to produce sure activation of the fluid actuatedclutch means without delays in oeration at high engine revolution rates,thereby eliminating shocks on the vehicle due to engine knockingproduced by starting and arresting the vehicle, especially with loadsthereon, at low engine revolution rates, and also eliminating delays inactivating the fluid actuated clutch means in the case of starting thevehicle suddenly on inclined areas at high engine revolution rate.

A second important object of the present invention is to provide ahydraulic pressure control system for fluid actuated clutch means havingan orifice and an accumulator disposed within a fluid conduit supplyingpressure fluid to the fluid actuated clutch means through theabove-mentioned regulator valve means, said accumulator providing suchhydraulic pressure for the fluid actuated clutch means in proportion tothe revolution rate of the prime engine of the vehicle, whereby toprevent slipping of wet clutch plates within the fluid actuated clutchmeans.

A third important object of the present invention is to provide ahydraulic pressure control system for fluid actuated clutch means inwhich enough fluid is obtained for the wet clutch plates of the fluidactuated clutch means as coolant therefor and for the torque converterto hold a certain value of hydraulic pressure therein even with lowhydraulic pressure in a pressure chamber of the regulator valve means.

A fourth important object of the present invention is to provide ahydraulic control system for fluid actuated clutch means having acontrol valve operatively connected with the regulator valve means, saidcontrol valve being activated by a brake pedal of the vehicle, so as toregulate operation of said regulator valve means in response toactivation of the brake pedal, whereby full activation of the brakepedal makes the fluid actuated clutch means de-activated to preventundesired slipping of the wet clutch plates.

A further important object of the present invention is to provide ahydraulic control system for fluid actuated clutch means which can beconstructed simply and unexpensively, with sure and smooth operations.

The novel features that are considered characteristic of thepresentinvention are set forth with particularity in the appendedclaims. The invention, itself, however, both as to its construction andits method of operation, together with additional objects and advantagesthereof, will best be understood from the following description of thespecific embodiments when read in connection with the accompanyingdrawings.

In the drawings:

FIG. 1 is a diagrammatic view, with parts in vertical crosssection, ofone embodiment of a system constructed in accordance with the presentinvention.

FIG. 2 is a characteristic curve showing the relationship betweenhydraulic pressure for the fluid actuated clutch means and the primeengine revolution rate, referring to the embodiment shown in FIG. 1.

FIG. 3 is a diagrammatic view, with parts in vertical crosssection, ofanother embodiment of a system constructed in accordance with thepresent invention.

FIG. 4 shows characteristic curves of the relationship between hydraulicpressure for the fluid actuated clutch means and the prime enginerevolution rate, referring to the embodiment shown in FIG. 3.

Described below is an embodiment of a device constructed in accordancewith the present invention. Referring to FIG. 1, a regulator valve means3 comprises a housing 4 which forms a bore 6 therein, a spool valve 7 isengaged reciprocatably to the axial direction thereof in the bore 6, anda coil spring 15 is installed in the bore 6 to bias the spool valve 7leftwardly. The spool valve 7 is provided thereon with lands l2, l3 and14 which divide the bore 6 into pressure chambers 8 and 9 and drainchambers 10 and 11. An inlet port 5 is provided in the wall of thehousing and is connected to a hydraulic pressure pump 1 through aconduit 2, said pump 1 being driven by the prime engine of the vehicle.A drain opening 16 communicates with the drain chamber 11 to producesmoother rightward movements of the spool valve 7. An orifice l7provided'through the land 12 of thespool valve 7 connects the pressurechambers 8 and 9 with each other. A slant passageway 18 passes throughthe spool valve 7, connecting the pressurechamber 9 with the drainchamber 10. A land 19 with a smaller diameter than those of the landsl2, l3 and 14 is provided adjacent the left side of the land 13 of thespool valve 7 approximately at the central portion thereof. The land 19forms an orifice with respect to an outlet port 21 which connects thepressure chamber 9 with a torque converter means 20 through a conduit22. The torque converter means 20 is further connected with a reliefvalve means 24 through a conduit 23. The relief valve means 24 comprisesa housing 25, a control ball 27, and a spring 28 biasing the controlball upwardly within a bore 26 of the housing 25. The control ball 27normally closes the conduit 23 to hold hydraulic pressure within thetorque converter means 20 up to a predetermined value. When thehydraulic pressure within the torque converter means 20 exceeds the saidpredetermined value, the relief valve means 24 opens to connect theconduit 23 to a conduit 29 and consequently to a reservoir 30. An outletport 31 is provided on the housing 4 of the regulator valve means 3 andis connected with a manual control valve means 35 through a conduit 32,supplying the manual control valve means 35 with modulated hydraulicpressure from the regulator valve means 3. The manual control valvemeans 35 controls selection of fluid actuated clutch means 33 and 34which are in communication with the manual control valve means 35,respectively, through conduits 36 and 37. When rightward movements ofthe spool valve 7 are made, overcoming the spring 15, the land 19 of thespool valve 7 faces a drain port 38 of the housing 4 to hold a certainvalue of hydraulic pressure in the pressure chamber 9.

The operation of the preferred embodiment described above will becomeclear from the following description. When the prime engine of thevehicle runs at approximately 500 revolutions per minute, an idlingrevolution rate, the hydraulic pressure pump 1 supplies pressure fluidat the rate of between and 20 liters per minute to pressure chamber 9.This rate of pressure fluid flow is too small to operate the regulatorvalve means 3, and thus, the spool valve 7 remains in its normalposition, under the biasing force of the spring 15. With the quantity offlow reduced by the orifice defined by the land 19 relative to theoutput port 21, pressure fluid flows into the torque converter means 20through the outlet port 21 and the conduit 22 to lubricate the torqueconverter means 20. The pressure fluid reaches the relief valve means 24through the conduit 23, modulated to about 1.5 kilograms per squarecentimeter, which is proper for the inside pressure of the torqueconverter means 20. At the same time, a certain amount of pressure fluidin the pressure chamber 9 runs into the drain chamber 10 through theslant passageway 18 to decrease hydraulic pressure in the pressurechamber 9. The diameter of the slant passageway is between 1.5 and 2.5millimeters, which, in turn, holds hydraulic pressure in the pressurechamber 9 at between 2.5 and 3 kilograms per square centimetenThishydraulic pressure is supplied to the manual control valve means 35through the outlet port 31 and the conduit 32 to create shocklessclutching operation of the clutch means 33 or 34. An acceleration ofengine rotation approximately up to 1,000 revolutions penninuteincreases the quantity of pressure fluid discharged from the hydraulicpressure pump 1, the pressure fluid being supplied to the pressurechamber 9 through the conduit 2. Now the quantity of this pressure fluidexceeds the total quantity that flows out of the pressure chamber 9through the slant passageway 18 and the orifice formed by the land 19.This causes the pressure fluid to pass to the pressure chamber 8 by wayof the orifice 17 of the land 12 on the spool valve 7. The spool. valve7 consequently moves rightward, overcoming the biasing force of thespring by the difference of the pressure-receiving areas. As a result,the land 19 moves to face the drain opening 38 and hydraulic pressure inthe pressure chamber 9 is modulated to be approximately 8 kilograms persquare centimeter. The pressure fluid is then delivered to the manualcontrol valve means 35 through the outlet port 31 and the conduit 32 toproduce engagement of the clutch means 33 or 34.

The relation between the number of engine revolutions and the hydraulicpressure in the clutch means 33 and 34 is further explained by thecharacteristic curve in FIG. 2. The hydraulic pressure in the clutchmeans 33 and 34 is kept rather low when the prime engine of the vehicleruns at around the idling revolution rate. This eliminates most of theshock force on the vehicle at starting movements thereof. In thenecessity of urgent starts, such inconvenience of delays of operationcan be eliminated by shifting the selector of the manual control valvemeans 35 after the prime engine is accelerated up to about 1 ,000revolutions per minute.

Described below, referring to FIGS. 3 and 4, is another embodiment ofthe device constructed in accordance with the present invention. Ahydraulic pressure pump 1 communicates with a torque converter means 2'at the impeller side thereof. Pressure fluid discharged from the pump 1is divided and part is delivered to an inlet port 5' of a regulatorvalve means 4' controlling operation of fluid actuated clutch means 90and 9b through a conduit 3, and part to the torque con verter means 2'through a conduit 6 and necessarily a restricted orifice 7' providedwithin the conduit 6. The latter part of the pressure fluid goes throughthe torque converter means 2 and then flows through a relief valve means8' into the clutch means 9a and 9b as coolant for wet clutch plates9',9'. The clutch means 9a is employed to advance the vehicle, and theclutch means 9b is employed to reverse the vehicle. 1

The regulator valve means 4' comprises a housing 4a which forms a bore10, a spool valve 11 is engaged reciprocatably to the axial directionthereof in the bore 10', and a coil spring 12 is installed in the bore10 to bias the spool valve 11' rightwardly. The spool valve 11' isprovided thereon with lands 13, 14 and 15' which divide the bore 11 intochambers 18', 19', 20' and 21. Also, a land 17' is provided adjacent theright side of the land 14, the diameter of the land 17' being smallerthan that of the bore 10' to form an orifice 16. The chambers 18 and 19'are always open to a reservoir 24 respectively, by means of outlet ports22 and 23'. The chamber 20' is a pressure chamber to allow pressurefluid-flow therein through the inlet port 5 and to deliver it to amanual control valve means 26 through an outlet port 25. A slantpassageway 27 passes through the spool valve 1], connecting the pressurechamber 20 to the chamber 19'. The chamber 20' is, at the same time,connected with the pressure chamber 21' through an orifice 28' providedin the land 15 of the spool valve 11. A rotary control valve means 30'communicates with the pressure chamber 20 through a port 29', beingoperated in response to stepping force applied onto a brake pedal (notshown in the Figure). The regulator valve means 4'.

becomes inoperative while the brake system of the vehicle is inoperation, since pressure fluid in the pressure chamber 20' returns tothe reservoir 24' through the rotary control valve means 30'. Pressurefluid discharged from an outlet port 25' of the regulator valve means 4flows into the manual control valve means 26' through a conduit 31', anorifice 32' disposed within the conduit 31 and an inlet port 33 of themanual control means 26, said orifice 32 reducing the quantity of thepressure fluid. At the same time, the pressure fluid mentioned isdivided and delivered to an accumulator 35 through a branch conduit 34'.

The manual control valve means 26' is employed to select the forwardclutch means 9a, or the reverse clutch means 9b and is operated by aselector lever (not shown in the Figure). The manual control valve means26 has a bore 36' in which a spool valve 37 is engaged reciprocatably tothe axial direction thereof. The spool valve 37 is provided with lands38 and 39 forming chambers 40, 41 and 42 within the bore 36'. The

chambers 40 and 42 are always open to the reservoir 24,

respectively, by means of outlet ports 43 and 44. The chamber 41 is apressure chamber, and outlet ports 45 and 46 thereof are connected,respectively, to the servo-cylinders (not shown in the Figure) of theforward clutch means 9a and the reverse clutch means 9b.

While the spool valve 37' is kept in its neutral position by a ball 49,the conduits 47 and 48 are open, respectively, to a port 52 of thechamber 40 and a port 53 of the chamber 42, respectively, through branchconduits 50 and 51 thereof. Under these condition, therefore, pressurefluid flows into the pressure chamber 41 through the inlet port 33' and,in turn, to the conduits 47 and 48 through the outlet ports 45 and 46.The branch conduits 50 and 51, respectively, belonging to the conduits47 and 48 lead the pressure fluid into the chambers 40 and 42 andconsequently to the reservoir 24' through the outlet ports 43 and 44.The result is, therefore, that no hydraulic pressure is produced in theservo-cylinders of the clutch means 9a and 9b, whereby to keep thevehicle steady.

When the spool valve 37 of the manual control valve means 26' is shiftedrightwardly, the ports 45 and 53 are closed,

respectively, by the lands 38 and 39 of the spool valve 37. The pressurefluid can be supplied from the pressure chamber 41 to the servo-cylinderof the forward clutch means 9a through the outlet port 46 and theconduit 48. This produces forward movement of the vehicle.

The leftward shift of the spool valve 37' of the manual control valvemeans 26 works to close the ports 46 and 52, respectively, by the lands39 and 38' of the spool valve 37'. Thus, supply of the pressure fluidfrom the pressure chamber 41 to the servo-cylinder of the reverse clutchmeans 9b is enabled through the outlet port 45 and the conduit 47,whereby to reverse the vehicle. Reference numeral 54 shows the primeengine, forward and reverse gears being shown respectively by referencenumerals 55 and 56. An output-shaft gear 57 is engaged with the forwardgear 55 to drive an output shaft 58. An idler gear 59 is engaged withthe reverse gear 56 and also the output-shaft gear 57, to transferdriving force of the reverse gear 56 to the output-shaft 58.

The operation of the above-mentioned embodiment of the device inrelation with the present invention is to be described hereafter furtherin detail. The hydraulic pressure pump 1 discharges pressure fluid inproportion to the revolution rate of the prime engine 54. This pressurefluid flows into the pressure chamber 20' by way of the inlet port 5' ofthe regulator valve means 4 and the orifice 16' formed between the land17 of the spool valve 11 and the inside wall surface of the bore of theregulator valve means 4'.

While the revolution rate of the prime engine 54 is rather low, forexample, from 600 to 1,500 revolutions per minute, the hydraulicpressure pump 1 discharges a small quantity of pressure fluid. Underthis condition, most of the pressure fluid in the pressure chamber isdrained out through the slant passageway 27' of the spool valve 11 andthe chamber 19. The spool valve 11 remains, therefore, unmoved, stayingin the position shown in FIG. 1. Thus, the hydraulic pressure in thepressure chamber 20' remains at a low value, and pressure fluid from thepressure chamber 20 goes into the manual control valve means 26' throughthe outlet port the conduit 31, the orifice 32 and the inlet port 33 ofthe manual control valve means 26. A portion of the pressure fluid is,on its way, led to the accumulator 35 by way of the orifice 32 and thebranch conduit 34', the accumulator 35 working to keep hydraulicpressure to be supplied to the fluid actuated clutch means 9a and 9b atsuch a value as not to let the wet clutch plates 9,9' slip. Thisprovides smooth engagement of the forward clutch means 911 or thereverse clutch means 9b, whereby to decrease shocks of the vehicle atits starts. At the same time, fluid as coolant for the wet clutch plates9',9' runs into the clutch means 90 and 9b through a conduit 6' and anorifice 7' disposed within the conduit 6, the orifice l6 preventing itfrom flowing into the inlet port 5 through the main conduit 3'.

When the rotation rate of the prime engine 54 goes up over 1500revolutions per minute, the quantity of pressure fluid discharged fromthe hydraulic pressure pump 1 is accordingly increased. The slantpassageway 27 become insufficient for draining out pressure fluid withinthe pressure chamber 20. The pressure fluid enters the chamber 21'through the orifice 28 to act on the right face of the spool valve 11',and the spool valve 11 is thus urged leftward, overcoming the biasingforce of the spring 12'. The land 14' of the spool valve 11 works tomake the outlet port 23' narrower and the pressure fluid in the pressurechamber 20 is drained out of the outlet port 23' through the orifice 16.At this moment, the hydraulic pressure within the pressure chamber 20'reaches the required predetermined value, regardless of the effects ofthe orifice 32' and the accumulator 35, enough hydraulic pressure beingnow supplied to either of the servo-cylinders (not shown in the Figure)of the forward clutch means 9a or the reverse clutch means 9b. Shocklessquick starts of the vehicle are, therefore, obtainable by stepping downon the accelerator pedal (not shown in the Figure).

Stepping down on the brake pedal (not shown in the Figure) operates therotary valve to drain out the pressure fluid within the pressure chamber20' of the regulator valve means 4' in accordance with the degree ofstepping-down force applied to the brake pedal. This returns the spoolvalve 11 toward the normal position shown in FIG. 3. This efi'ect can beobtained because the orifice 16' formed between the land 17' of thespool valve 11 and the inside wall of the bore 10' is predetermined tomaintain a stable condition regardless of the increase of the quantityof pressure fluid discharged from the hydraulic pressure pump 1 by theacceleration of the prime engine revolution rate. Thus, the hydraulicpressure within the servo-cylinders of the forward and reverse clutchmeans 9a and 9b is regulated to be at a low figure to enablesemi-engagement of the clutch means 9a and 9b. When the brake pedal isreleased, the hydraulic pressure within the clutch means 9a and 9bincreases approximately in proportion to the revolution rate of theprime engine 54 until the revolution rate comes up to around 1,500revolutions per minute, as shown in FIG. 4 by the characteristic curveA. The hydraulic pressure within the clutch means 9a and 9b iscontrolled to be above the minimum, as shown by the characteristic curveB at every increase so as not to cause undesired slipping of the wetclutch plates 9, 9'.

Although certain specific embodiments of the present invention have beenshown and described, it is obvious that many modifications thereof arepossible. The present invention, therefore, is not intended to berestricted to the exact showing of the drawings and description thereof,but is considered to include reasonable and obvious equivalents withinthe scope of the appended claims and without departing from, orexceeding the spirit of the invention.

What is claimed is:

1. In a hydraulic control system for a vehicle comprising firsthydraulic passage means connecting a source of pressure fluid to fluidactuated frictional engaging means, said source being provided withpressurizing means for providing pressurized fluid of the amount inproportion to the revolution rate of the prime engine of the vehicle,and a regulator valve means disposed within said first hydraulic passagemeans for controlling automatically hydraulic pressure supplied intosaid frictional engaging means therein, said regulator valve meanscomprising a housing forming a bore therein and having inside end walls,a spring installed within said bore, and a spool valve engaged in saidbore reciprocatably to the axial direction thereof and biased to anormal position thereof by said spring, said spool valve including aplurality of lands thereon, a first pressure-chamber, a seconddrain-chamber and a third chamber accommodating said spring therein, allof said chambers being formed by said spool valve within said housing,said first and second chambers being interconnected by a passagewaypassing through one of the lands, and a drain-port connected to saidsecond drain-chamber and controlled by said one of the lands, wherebywhen the pressure fluid source supplies said first pressure-chamber withlow pressure fluid, the pressure fluid is drained out therefrom throughsaid passageway, and when high pressure fluid is supplied to said firstpressure-chamber, the spool valve is urged to move, overcoming saidspring to keep a predetermined value of hydraulic pressure within thefirst pressure-chamber.

2. In a hydraulic control system as set forth in claim 1, wherein saidlands of said spool valve comprises a first, a second, and a third land,said first pressure-chamber is formed between the first land and thesecond land provided with said passageway, said second drain-chamber isformed between the second and third lands, said third chamber is formedbetween the third land and one inside end wall engaging said springtherein, and a fourth chamber is further formed between the first landand the other inside end wall, said first and fourth chambers beinginterconnected by an orifice passing through the first land.

3. In a hydraulic control system as set forth in claim 2, wherein asecond hydraulic passage means is provided for connecting said pressurefluid source to a torque converter, said second passage means includinga return conduit leading to a reservoir, and a relief valve means isfurther interposed within said second passage means for modulatingoutput hydraulic pressure from said torque converter, and said regulatorvalve means is disposed within said first and second passage means aheadof said fluid actuated frictional engaging means and said torqueconverter.

4. In a hydraulic control system as set forth in claim 3, wherein saidregulator valve means comprises a smaller diameter land being adjacentthe second land inside the first chamber and forming a further orificewith respect to the inside wall of the housing for controlling pressurefluid supplied into said second passage means connecting said firstchamber to said torque converter.

5. In a hydraulic control system as set forth in claim 3, wherein saidfrictional engaging means comprises a forward and a reverse fluidactuated clutch means, and a manual control valve means is disposedwithin said first passage means for controlling the selection of a pairof fluid passages connected said forward and reverse clutch means to anoutlet port of said regulator valve means, respectively.

6. In a hydraulic control system as set forth in claim 2, wherein asecond passage means is provided for connecting said pressure fluidsource to a torque converter, said second passage means being extendedto said fluid actuated clutch means, and a relief valve means is furtherdisposed within said second passage means between said torque converterand said frictional engaging means for modulating hydraulic pressurefrom said torque converter, and said regulator valve means is disposedwithin said first passage means.

7. In a hydraulic control system as set forth in claim 6, wherein anorifice and an accumulator are disposed within said first passage meansbetween said regulator valve means and said fluid actuated frictionalengaging means, said orifice being provided within said first passagemeans ahead of said accumulator.

8. In a hydraulic control system as set forth in claim 7,

wherein said frictional engaging means comprises a forward and a reversefluid actuated clutch means, and a manual control valve means isdisposed within said first passage means between said accumulator andsaid forward and reverse clutch means for controlling the selection of apair of fluid passages connected said forward and reverse clutch meansto an outlet port of said regulator valve means, respectively.

9. In a hydraulic control system as set forth in claim 6, wherein saidregulator valve means comprises a smaller diameter land being adjacentthe second land inside the first chamber and forming a further orificewith respect to the inside wall of the housing, whereby when thepressure fluid source supplies said first pressure-chamber with lowpressure fluid, the pressure fluid supplied through said first passagemeans is controlled by said orifice, and when said spool valve is urgedto move overcoming said spring, said drain-port is controlled by saidorifice.

10. In a hydraulic control system as set forth in claim 2, wherein acontrol valve means is provided in communication with an outlet portprovidedin the first chamber of said regulator valve means, said controlvalve means being operatively connected to a brake pedal of the vehicle,whereby full activation of the brake pedal makes said frictionalengaging means de-activated since pressure fluid is drained out of theregulator valve means into a reservoir connected to said control valvemeans.

1. In a hydraulic control system for a vehicle comprising firsthydraulic passage means connecting a source of pressure fluid to fluidactuated frictional engaging means, said source being provided withpressurizing means for providing pressurized fluid of the amount inproportion to the revolution rate of the prime engine of the vehicle,and a regulator valve means disposed within said first hydraulic passagemeans for controlling automatically hydraulic pressure supplied intosaid frictional engaging means therein, said regulator valve meanscomprising a housing forming a bore therein and having inside end walls,a spring installed within said bore, and a spool valve engaged in saidbore reciprocatably to the axial direction thereof and biased to anormal position thereof by said spring, said spool valve including aplurality of lands thereon, a first pressurechamber, a seconddrain-chamber and a third chamber accommodating said spring therein, allof said chambers being formed by said spool valve within said housing,said first and second chambers being interconnected by a passagewaypassing through one of the lands, and a drain-port connected to saidsecond drain-chamber and controlled by said one of the lands, wherebywhen the pressure fluid source supplies said first pressure-chamber withlow pressure fluid, the pressure fluid is drained out therefrom throughsaid passageway, and when high pressure fluid is supplied to said firstpressure-chamber, the spool valve is urged to move, overcoming saidspring to keep a predetermined value of hydraulic pressure within thefirst pressure-chamber.
 2. In a hydraulic control system as set forth inclaim 1, wherein said lands of said spool valve comprises a first, asecond, and a third land, said first pressure-chamber is formed betweenthe first land and the second land provided with said passageway, saidsecond drain-chamber is formed between the second and third lands, saidthird chamber is formed between the third land and one inside end wallengaging said spring therein, and a fourth chamber is further formedbetween the first land and the other inside end wall, said first andfourth chambers being interconnected by an orifice passing through thefirst land.
 3. In a hydraulic control system as set forth in claim 2,wherein a second hydraulic passage means is provided for connecting saidpressure fluid source to a torque converter, said second passage meansincluding a return conduit leading to a reservoir, and a relief valvemeans is further interposed within said second passage means formodulating output hydraulic pressure from said torque converter, andsaid regulator valve means is disposed within said first and secondpassaGe means ahead of said fluid actuated frictional engaging means andsaid torque converter.
 4. In a hydraulic control system as set forth inclaim 3, wherein said regulator valve means comprises a smaller diameterland being adjacent the second land inside the first chamber and forminga further orifice with respect to the inside wall of the housing forcontrolling pressure fluid supplied into said second passage meansconnecting said first chamber to said torque converter.
 5. In ahydraulic control system as set forth in claim 3, wherein saidfrictional engaging means comprises a forward and a reverse fluidactuated clutch means, and a manual control valve means is disposedwithin said first passage means for controlling the selection of a pairof fluid passages connected said forward and reverse clutch means to anoutlet port of said regulator valve means, respectively.
 6. In ahydraulic control system as set forth in claim 2, wherein a secondpassage means is provided for connecting said pressure fluid source to atorque converter, said second passage means being extended to said fluidactuated clutch means, and a relief valve means is further disposedwithin said second passage means between said torque converter and saidfrictional engaging means for modulating hydraulic pressure from saidtorque converter, and said regulator valve means is disposed within saidfirst passage means.
 7. In a hydraulic control system as set forth inclaim 6, wherein an orifice and an accumulator are disposed within saidfirst passage means between said regulator valve means and said fluidactuated frictional engaging means, said orifice being provided withinsaid first passage means ahead of said accumulator.
 8. In a hydrauliccontrol system as set forth in claim 7, wherein said frictional engagingmeans comprises a forward and a reverse fluid actuated clutch means, anda manual control valve means is disposed within said first passage meansbetween said accumulator and said forward and reverse clutch means forcontrolling the selection of a pair of fluid passages connected saidforward and reverse clutch means to an outlet port of said regulatorvalve means, respectively.
 9. In a hydraulic control system as set forthin claim 6, wherein said regulator valve means comprises a smallerdiameter land being adjacent the second land inside the first chamberand forming a further orifice with respect to the inside wall of thehousing, whereby when the pressure fluid source supplies said firstpressure-chamber with low pressure fluid, the pressure fluid suppliedthrough said first passage means is controlled by said orifice, and whensaid spool valve is urged to move overcoming said spring, saiddrain-port is controlled by said orifice.
 10. In a hydraulic controlsystem as set forth in claim 2, wherein a control valve means isprovided in communication with an outlet port provided in the firstchamber of said regulator valve means, said control valve means beingoperatively connected to a brake pedal of the vehicle, whereby fullactivation of the brake pedal makes said frictional engaging meansde-activated since pressure fluid is drained out of the regulator valvemeans into a reservoir connected to said control valve means.